Polymer matrix composites comprising dielectric particles and methods of making the same

ABSTRACT

A polymer matrix composite comprising a porous polymeric network; and a plurality of dielectric particles distributed within the polymeric network structure; wherein the dielectric particles are present in a range from 5 to 98 weight percent, based on the total weight of the dielectric particles and the polymer (excluding the solvent); and wherein the polymer matrix composite has a dielectric constant in a range from 1.05 to 80; and methods for making the same. Polymer matrix composites comprising dielectric particles are useful, for example, as electric field insulators.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 62/587,045, filed Nov. 16, 2017, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND

Typically, polymeric binders have a relatively low dielectric constant, but greater than air (typically, in a range from greater than 2 to less than 4). Therefore, a large volume of dielectric articles in the binder is typically used to get a high enough dielectric constant to support an electric field in a capacitive device. There is a need for insulating materials, useful in electronic devices that have a high dielectric constant with low dielectric loss, but also have very low electrical conductivity. Electronic devices such as capacitors, actuators, artificial muscles and organs, smart materials and structures, micro-electro-mechanical (MEMS) devices, micro-fluidic devices, acoustic devices and sensors, which are capacitive devices, have increased the need for a variety of new and better insulating materials. There is also a need in the field of electronic devices for simpler, more economical, manufacturing processes to produce such devices. It would further be desirable to provide dielectric articles that can eliminate or reduce shorting between adjacent bumps or interconnection patterns by preventing aggregation of particles. It is also desirable to provide dielectric articles having superior solvent resistance.

SUMMARY

In one aspect, the present disclosure describes a polymer matrix composite comprising:

a porous polymeric network structure; and

a plurality of dielectric particles distributed within the polymeric network structure, wherein the dielectric particles are present in a range from 5 to 98 (in some embodiments, 10 to 98, 20 to 98, 25 to 98, 50 to 98, 75 to 98, 80 to 98, 90 to 98, or even 95 to 98) weight percent, based on the total weight of the dielectric particles and the polymer (excluding any solvent); and wherein the polymer matrix composite has an overall dielectric constant in a range from 1.05 to 80 (in some embodiments, in a range from 1.1 to 80, 1.15 to 80, 1.2 to 80, 1.1 to 75, 1.15 to 75, 1.2 to 75, 1.2 to 70, 1.1 to 70, 1.15 to 70, 1.2 to 65, 1.1 to 65, 1.15 to 65, 1.2 to 60, 1.1 to 60, 1.15 to 60, 1.2 to 55, 1.1 to 55, 1.15 to 55, 1.2 to 50, 1.1 to 50, 1.15 to 50, 1.2 to 45, 1.1 to 45, 1.15 to 45, 1.2 to 40, 1.1 to 40, 1.15 to 40, 1.2 to 35, 1.1 to 35, 1.15 to 35, 1.2 to 30, 1.1 to 30, 1.15 to 30, 1.2 to 25, 1.1 to 25, 1.15 to 25, 1.2 to 20, or even 1.1 to 20, 1.15 to 20, 1.2 to 20). “Dielectric particles,” as used herein, refer to particles that have an intrinsic relative dielectric constant of 1.05 to 80.

In another aspect, the present disclosure describes a first method of making polymer matrix composites described herein, the method comprising:

(e.g., mixing or blending) a thermoplastic polymer, a solvent, and a plurality of dielectric particles to provide a slurry;

forming the slurry in to an article (e.g., a layer);

heating the article in an environment to retain at least 90 (in some embodiments, at least 91, 92, 93, 94, 95, 96, 97, 98, 99, or even at least 99.5) percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) percent of the thermoplastic polymer, based on the total weight of the thermoplastic polymer; and

inducing phase separation of the thermoplastic polymer from the solvent to provide the polymer matrix composite.

In another aspect, the present disclosure describes a second method of making polymer matrix composites described herein, the method comprising:

combining (e.g., mixing or blending) a thermoplastic polymer, a solvent for the thermoplastic polymer, and a plurality of dielectric particles to form a miscible thermoplastic polymer-solvent solution;

inducing phase separation of the thermoplastic polymer from the solvent; and

removing at least a portion of the solvent to provide the polymer matrix composite.

“Miscible” as used herein refers to the ability of substances to mix in all proportions (i.e., to fully dissolve in each other at any concentration), forming a solution, wherein for some solvent-polymer systems heat may be needed for the polymer to be miscible with the solvent. By contrast, substances are immiscible if a significant proportion does not form a solution. For example, butanone is significantly soluble in water, but these two solvents are not miscible because they are not soluble in all proportions.

“Phase separation,” as used herein, refers to the process in which particles are uniformly dispersed in a homogeneous polymer-solvent solution that is transformed (e.g., by a change in temperature or solvent concentration) into a continuous three-dimensional polymer matrix composite. In the first method, the desired article is formed before the polymer becomes miscible with the solvent and the phase separation is a thermally induced phase separation (TIPS) process. In the second method, the polymer is miscible with the solvent before the desired article is formed. In the second method, phase separation is achieved via solvent induced phase separation (SIPS) using a wet or dry process, or thermally induced phase separation methods.

In the SIPS wet process, the solvent dissolving the polymer is exchanged with a nonsolvent to induce phase separation. The new exchanging solvent in the system becomes the pore former for the polymer. In the SIPS dry process, the solvent dissolving the polymer is evaporated to induce phase separation. In the dry process, a nonsolvent is also solubilized in the solution by the solvent dissolving the polymer. This nonsolvent for the polymer becomes the pore former for the polymer as the solubilizing solvent evaporates. The process is considered a “dry process” because no additional exchange liquids are used. The nonsolvent is also normally volatile but has a boiling point at least 30° C. lower than the solvent.

In the TIPS process, elevated temperature is used to make a nonsolvent become a solvent for the polymer, then the temperature is lowered returning the solvent to a nonsolvent for the polymer. Effectively, the hot solvent becomes the pore former when sufficient heat is removed and it loses its solvating capacity. The solvent used in the thermal phase separation process can be volatile or nonvolatile.

Surprisingly, in the first method to make a polymer matrix composite, the relatively high particle loadings allow a slurry to be made that can be shaped into a layer, that maintains its form as the solvent is heated to become miscible with the polymer. The solvent used is normally volatile and is later evaporated. In the second method using TIPS process to make a polymer matrix composite, the solvent used is normally nonvolatile. In the second method to make a polymer matrix composite by the wet or dry SIPS process, the solvents are normally nonvolatile for the wet process and volatile for the dry process.

Typically, the maximum particle loading that can be achieved in traditional particle-filled composites (e.g., dense polymeric films and adhesives), is not more than about 40 to 60 vol. %, based on the volume of the particles and binder. Incorporating more than 60 vol. % particles into traditional particle-filled composites typically is not achievable because such high particle loaded materials cannot be processed via coating or extrusion methods and/or the resulting composite becomes very brittle. Traditional composites also typically fully encapsulate the particles with binder preventing high packing densities. Surprisingly, the high levels of solvent and the phase separated morphologies obtained with the methods described herein enable relatively high particle loadings with relatively low amounts of high molecular weight binder. The high particle loading also helps minimize the formation of thin non-porous polymer layer that can form during phase separation. Moreover, the polymer matrix composites described herein are relatively flexible, and tend not to shed particles. Although not wanting to be bound by theory, in the case of electrically non-conductive (i.e., having an electrical resistance of at least 40 mega ohms) dielectric particles, it is believed that another advantage of embodiments of polymer matrix composite described herein, is that the particles are not fully coated with binder, enabling a high degree of particle surface contact, and composite density, while maintaining flexibility after compression. Surprisingly, in some embodiments, after compression some dielectric particle containing polymer matrix composites can show an increase in dielectric constant. The high molecular weight binder also does not readily flow in the absence of solvent, even at elevated temperatures (e.g., 135° C.).

In some embodiments, an advantage of polymer matrix composites described herein with relatively high dielectric particle loadings is their dielectric constant is higher than conventional polymer matrix composites having lower particle loadings.

The ability to fabricate electromagnetic (EM) materials with graded dielectric properties benefits a variety of interesting applications (e.g., low-profile antennas, antireflective surfaces, passive beam formers (e.g., Luneburg lenses), graded index lenses, and structural and armored radomes). These applications typically utilize a variety of dielectric constant layers with the low-end close to that of air, which has a dielectric constant of 1. Although not wanting to be bound by theory, it is believed that this enables impedance matching for the electromagnetic waves to travel through the layers instead of scattering or reflecting off the medium.

Polymer matrix composites described herein provide relatively highly loaded, low-density composite layers that can have a range of tunable dielectric constants.

Polymer matrix composites comprising dielectric particles are useful, for example, as electric field insulators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing a scanning electron microscope (SEM) micrograph of a cross-section of an exemplary polymer matrix composite (Example 1) described herein.

FIG. 2 is a schematic showing a scanning electron microscope (SEM) micrograph of a cross-section of an exemplary polymer matrix composite (Example 13) described herein.

FIG. 3 is a schematic showing a scanning electron microscope (SEM) micrograph of a cross-section of an exemplary polymer matrix composite (Example 14) described herein.

DETAILED DESCRIPTION

The dielectric particles are present in a range from 5 to 98, 10 to 98, 20 to 98, 25 to 98, 50 to 98, 75 to 98, 80 to 98, 90 to 98, or even 95 to 98) weight percent, based on the total weight of the dielectric particles and the polymer (excluding any solvent).

Exemplary dielectric particles include inorganic particles, or coated (e.g., with metal and metal oxides) glass microspheres or bubbles. Exemplary dielectric particles include inorganic (e.g., ceramic) dielectric particles comprise at least one of barium titanate, alumina, titania, or CaCu₃Ti₄O₁₂.

Exemplary sizes of the dielectric particles range from 10s of nanometers to 100s of micrometers in size. Exemplary shapes of the dielectric particles include irregular, platy, spherical shapes, and as well as agglomerated forms. Agglomerates can range in size, for example, from a few micrometers up to and including a few millimeters. The particles can be mixed to have multimodal size distributions which may, for example, allow for optimal packing density.

In some embodiments, the dielectric particles have an average particle size (average length of longest dimension) in a range from 10 nm to 120 micrometers (in some embodiments, in a range from 50 nm to 100 nm, 15 micrometers to 125 micrometers, or even 30 micrometers to 60 micrometers).

In some embodiments, the dielectric particles have bimodal or trimodal distribution. Multimodal distributions of particles can allow for higher packing efficiency, improved particle to particle contact.

Although not wanting to be bound by theory, it is believed that the effect of particles on the relative dielectric constant of a polymer matrix may be predicted by the rule of mixtures (see Materials Science and Polymers for Engineers, Oswald et al., pp. 494-496, 2012).

$ɛ_{eff} = {ɛ_{m}\left( {1 - {3\varnothing \frac{ɛ_{m} - ɛ_{p}}{{2ɛ_{m}} + ɛ_{p}}}} \right)}$

where ø is the volume fraction of the dielectric particles in the matrix, ε_(eff), ε_(m) and ε_(p) are the relative dielectric constants of polymer matrix composite, polymer matrix, and the dielectric particles, respectively.

As-made polymer matrix composites described herein (i.e., prior to any compression or other post formation densification) typically have a density in a range from 0.05 to 6 (in some embodiments, in a range from 0.05 to 3, 0.05 to 2.5, 0.05 to 2, 0.05 to 1, or even 0.05 to 0.2) g/cm³.

In some embodiments, compressed polymer matrix composites have a density of at least 1 (in some embodiments, at least 4, or even at least 6; in some embodiments, in a range from 1 to 6, or even 4 to 6) g/cm³.

In some embodiments, polymer matrix composites described herein have a porosity of at least 5 (in some embodiments, at least 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90; in some embodiments, in a range from 25 to 90) percent.

The polymeric network structure may be described as a porous polymeric network or a porous phase separated polymeric network. Generally, the porous polymeric network (as-made) includes an interconnected porous polymeric network structure comprising a plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs). The interconnected polymeric structures may adhere directly to the surface of the particles and act as a binder for the particles. In this regard, the space between adjacent particles (e.g., particles or agglomerate particles) may include porous polymeric network structures, as opposed to a solid matrix material, thereby providing desired porosity.

In some embodiments, the polymeric network structure may include a 3-dimensional reticular structure that includes an interconnected network of polymeric fibrils. In some embodiments, individual fibrils have an average width in a range from 10 nm to 100 nm (in some embodiments, in a range from 100 nm to 500 nm, or even 500 nm to 5 micrometers).

In some embodiments, the particles are dispersed within the polymeric network structure, such that an external surface of the individual units of the particles (e.g., individual particles or individual agglomerate particles) is mostly uncontacted, or uncoated, by the polymeric network structure. In this regard, in some embodiments, the average percent areal coverage of the polymeric network structure on the external surface of the individual particles (i.e., the percent of the external surface area that is in direct contact with the polymeric network structure) is not greater than 50 (in some embodiments, not greater than 40, 30, 25, 20, 10, 5, or even not greater than 1) percent, based on the total surface area of the external surfaces of the individual particles.

In some embodiments, the polymeric network structure does not penetrate internal porosity or internal surface area of the individual particles (e.g., individual particles or individual agglomerate particles) is mostly uncontacted, or uncoated, by the polymeric network structure.

In some embodiments, the polymeric network structure may comprise, consist essentially of, or consist of at least one thermoplastic polymer. Exemplary thermoplastic polymers include polyurethane, polyester (e.g., polyethylene terephthalate, polybutylene terephthalate, and polylactic acid), polyamide (e.g., nylon 6, nylon 6,6, nylon 12 and polypeptide), polyether (e.g., polyethylene oxide and polypropylene oxide), polycarbonate (e.g., bisphenol-A-polycarbonate), polyimide, polysulphone, polyethersulphone, polyphenylene oxide, polyacrylate (e.g., thermoplastic polymers formed from the addition polymerization of monomer(s) containing an acrylate functional group), polymethacrylate (e.g., thermoplastic polymers formed from the addition polymerization of monomer(s) containing a methacrylate functional group), polyolefin (e.g., polyethylene and polypropylene), styrene and styrene-based random and block copolymer, chlorinated polymer (e.g., polyvinyl chloride), fluorinated polymer (e.g., polyvinylidene fluoride; copolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; copolymers of ethylene, tetrafluoroethylene; hexafluoropropylene; and polytetrafluoroethylene), and copolymers of ethylene and chlorotrifluoroethylene. In some embodiments, thermoplastic polymers include homopolymers or copolymers (e.g., block copolymers or random copolymers). In some embodiments, thermoplastic polymers include a mixture of at least two thermoplastic polymer types (e.g., a mixture of polyethylene and polypropylene or a mixture of polyethylene and polyacrylate). In some embodiments, the polymer may be at least one of polyethylene (e.g., ultra-high molecular weight polyethylene), polypropylene (e.g., ultra-high molecular weight polypropylene), polylactic acid, poly(ethylene-co-chlorotrifluoroethylene) and polyvinylidene fluoride. In some embodiments, the thermoplastic polymer is a single thermoplastic polymer (i.e., it is not a mixture of at least two thermoplastic polymer types). In some embodiments, the thermoplastic polymers consist essentially of, or consist of polyethylene (e.g., ultra-high molecular weight polyethylene).

In some embodiments, the thermoplastic polymer used to make the polymer matrix composites described herein are particles having a particle size less than 1000 (in some embodiments, in the range from 1 to 10, 10 to 30, 30 to 100, 100 to 200, 200 to 500, 500 to 1000) micrometers.

In some embodiments, the porous polymeric network structure comprises at least one of polyacrylonitrile, polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyphenylene oxide, polyacrylate, polymethacrylate, polyolefin, styrene or styrene-based random and block copolymer, chlorinated polymer, fluorinated polymer, or copolymers of ethylene and chlorotrifluoroethylene.

In some embodiments, the porous polymeric network structure comprises a polymer having a number average molecular weight in a range from 5×10⁴ to 1×10⁷ (in some embodiments, in a range from 1×10⁶ to 8×10⁶, 2×10⁶ to 6×10⁶, or even 3×10⁶ to 5×10⁶) g/mol. For purposes of the present disclosure, the number average molecular weight can be measured by known techniques in the art (e.g., gel permeation chromatography (GPC)). GPC may be conducted in a suitable solvent for the thermoplastic polymer, along with the use of narrow molecular weight distribution polymer standards (e.g., narrow molecular weight distribution polystyrene standards). Thermoplastic polymers are generally characterized as being partially crystalline, exhibiting a melting point. In some embodiments, the thermoplastic polymer may have a melting point in a range from 120 to 350 (in some embodiments, in a range from 120 to 300, 120 to 250, or even 120 to 200) ° C. The melting point of the thermoplastic polymer can be measured by known techniques in the art (e.g., the on-set temperature measured in a differential scanning calorimetry (DSC) test, conducted with a 5 to 10 mg sample, at a heating scan rate of 10° C./min., while the sample is under a nitrogen atmosphere).

In some embodiments, the polymeric network structure is a continuous network structure (i.e., the polymer phase comprises a structure that is open cell with continuous voids or pores forming interconnections between the voids, extending throughout the structure). In some embodiments, at least 2 (in some embodiments, at least 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or even, 100) percent of the polymer network structure, by volume, may be a continuous polymer network structure. It should be noted that for purposes of the present disclosure, the portion of the volume of the polymer matrix composite made up of the particles is not considered part of the polymeric network structure. In some embodiments, the polymer network extends between two particles forming a network of interconnected particles.

The solvent (e.g., a first solvent) is selected such that it forms a miscible polymer-solvent solution. In some cases, elevated temperatures may be required to form the miscible polymer-solvent solution. The solvent may be a blend of at least two individual solvents. In some embodiments, when the polymer is a polyolefin (e.g., at least one of polyethylene and polypropylene), the solvent may be, for example, at least one of mineral oil, tetralin, decalin, orthodichlorobenzene, cyclohexane-toluene mixture, dodecane, paraffin oil/wax, kerosene, isoparaffinic fluids, p-xylene/cyclohexane mixture (1/1 wt./wt.), camphene, 1,2,4 trichlorobenzene, octane, orange oil, vegetable oil, castor oil, or palm kernel oil. In some embodiments, when the polymer is polyvinylidene fluoride, the solvent may be, for example, at least one of ethylene carbonate, propylene carbonate, or 1,2,3 triacetoxypropane. The solvent may be removed, for example, by evaporation. High vapor pressure solvents being particularly suited to this method of removal. If, however, the first solvent has a low vapor pressure, it may be desirable to have a second solvent, of higher vapor pressure, to extract the first solvent, followed by evaporation of the second solvent. For example, in some embodiments, when mineral oil is used as a first solvent, isopropanol at elevated temperature (e.g., about 60° C.) or a blend of methyl nonafluorobutyl ether (C₄F₉OCH₃), ethylnonafluorobutyl ether (C₄F₉OC₂H₅), and trans-1,2-dichloroethylene (available, for example, under the trade designation “NOVEC 72DE” from 3M Company, St. Paul, Minn.) may be used as a second solvent to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, when at least one of vegetable oil or palm kernel oil is used as the first solvent, isopropanol at elevated temperature (e.g., about 60° C.), may be used as the second solvent. In some embodiments, when ethylene carbonate is used as the first solvent, water may be used as the second solvent.

In some embodiments, small quantities of other additives can be added to the polymer matrix composite to impart additional functionality or act as processing aids. These include viscosity modifiers (e.g., fumed silica, block copolymers, and wax), plasticizers, thermal stabilizers (e.g., such as available, for example, under the trade designation “IRGANOX 1010” from BASF, Ludwigshafen, Germany), antimicrobials (e.g., silver and quaternary ammonium), flame retardants, antioxidants, dyes, pigments, and ultraviolet (UV) stabilizers.

In some embodiments, polymer matrix composites described herein, are in the form of a layer having a thickness in a range from 50 to 7000 micrometers, wherein the thickness excludes the height of any protrusions extending from the base of the layer.

In some embodiments, the porous polymeric network structure is produced by an induced phase separation of a miscible thermoplastic polymer-solvent solution. In some embodiments, induced phase separation is at least one of thermally induced phase separation or solvent induced phase separation.

First Method

A first method of making polymer matrix composites described herein comprises:

combining (e.g., mixing or blending) a thermoplastic polymer, a solvent, and a plurality of dielectric particles to provide a slurry;

forming the slurry in to an article (e.g., a layer);

heating the article in an environment to retain at least 90 (in some embodiments, at least 91, 92, 93, 94, 95, 96, 97, 98, 99, or even at least 99.5) percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) percent of the thermoplastic polymer, based on the total weight of the thermoplastic polymer; and

inducing phase separation of the thermoplastic polymer from the solvent to provide the polymer matrix composite.

If the particles are dense, typically the slurry is continuously mixed or blended to prevent or reduce settling or separation of the polymer and/or particles from the solvent. In some embodiments, the slurry is degassed using techniques known in the art to remove entrapped air.

The slurry can be formed in to an article using techniques known in the art, including knife coating, roll coating (e.g., roll coating through a defined nip), and coating through any number of different dies having the appropriate dimensions or profiles.

In some embodiments of the first method, combining is conducted at at least one temperature below the melting point of the polymer and below the boiling point of the solvent.

In some embodiments of the first method, heating is conducted at at least one temperature above the melting point of the miscible thermoplastic polymer-solvent solution, and below the boiling point of the solvent.

In some embodiments of the first method, inducing phase separation is conducted at at least one temperature less than the melting point of the polymer in the slurry. Although not wanting to be bound, it is believed that in some embodiments, solvents used to make a miscible blend with the polymer can cause melting point depression in the polymer. The melting point described herein includes below any melting point depression of the polymer solvent system.

In some embodiments of the first method, the solvent is a blend of at least two individual solvents. In some embodiments, when the polymer is a polyolefin (e.g., at least one of polyethylene or polypropylene), the solvent may be at least one of mineral oil, tetralin, decalin, orthodichlorobenzene, cyclohexane-toluene mixture, dodecane, paraffin oil/wax, kerosene, p-xylene/cyclohexane mixture (1/1 wt./wt.), camphene, 1,2,4 trichlorobenzene, octane, orange oil, vegetable oil, castor oil, or palm kernel oil. In some embodiments, when the polymer is polyvinylidene fluoride, the solvent is at least one of ethylene carbonate, propylene carbonate, or 1,2,3 triacetoxypropane.

In some embodiments of the first method, the polymeric network structure may be formed during phase separation. In some embodiments, the polymeric network structure is provided by an induced phase separation of a miscible thermoplastic polymer-solvent solution. In some embodiments, the phase separation is induced thermally (e.g., via thermally induced phase separation (TIPS) by quenching to a lower temperature than used during heating). Cooling can be provided, for example, in air, liquid, or on a solid interface, and varied to control the phase separation. The polymeric network structure may be inherently porous (i.e., have pores). The pore structure may be open, enabling fluid communication from an interior region of the polymeric network structure to an exterior surface of the polymeric network structure and/or between a first surface of the polymeric network structure and an opposing second surface of the polymeric network structure.

In some embodiments of the method described herein, the weight ratio of solvent to polymer is at least 9:1. In some embodiments, the volume ratio of particles to polymer is at least 9:1. In some embodiments, and for ease of manufacturing, it may be desirable to form a layer at room temperature. Typically, during the layer formation using phase separation, relatively small pores are particularly vulnerable to collapsing during solvent extraction. The relatively high particle to polymer loading achievable by the methods described herein may reduce pore collapsing and yield a more uniform defect-free polymer matrix composite.

In some embodiments, the first method further comprises removing at least a portion (in some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100 percent by weight of the solvent, based on the weight of the solvent in the formed article) of the solvent from the formed article, after inducing phase separation of the thermoplastic polymer from the solvent.

In some embodiments of the first method, at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article is removed, wherein the formed article, before removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, of the solvent has a first volume, wherein the formed article, after removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, has a second volume, and wherein the difference between the first and second volume (i.e., (the first volume minus the second volume) divided by the first volume times 100) is less than 10 (in some embodiments, less than 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.75, 0.5, or even less than 0.3) percent. Volatile solvents can be removed from the polymer matrix composite, for example, by allowing the solvent to evaporate from at least one major surface of the polymer matrix composite. Evaporation can be aided, for example, by the addition of at least one of heat, vacuum, or air flow. Evaporation of flammable solvents can be achieved in a solvent-rated oven. If the first solvent, however, has a low vapor pressure, a second solvent, of higher vapor pressure, may be used to extract the first solvent, followed by evaporation of the second solvent. For example, in some embodiments, when mineral oil is used as a first solvent, isopropanol at elevated temperature (e.g., about 60° C.) or a blend of methyl nonafluorobutyl ether (C₄F₉OCH₃), ethylnonafluorobutyl ether (C₄F₉OC₂H₅), and trans-1,2-dichloroethylene (available, for example, under the trade designation “NOVEC 72DE” from 3M Company, St. Paul, Minn.) may be used as a second solvent to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, when at least one of vegetable oil or palm kernel oil is used as the first solvent, isopropanol at elevated temperature (e.g., about 60° C.) may be used as the second solvent. In some embodiments, when ethylene carbonate is used as the first solvent, water may be used as the second solvent.

In some embodiments of the first method, the article has first and second major surfaces with ends perpendicular to the first and second major surfaces, and the ends are unrestrained (i.e., without the need for restraints during extraction) during the solvent removal. This can be done, for example, by drying a portion of a layer without restraint in an oven. Continuous drying can be achieved, for example, by drying a long portion of a layer supported on a belt as it is conveyed through an oven. Alternatively, to facilitate removal of non-volatile solvents, for example, a long portion of a layer can be continuously conveyed through a bath of compatible volatile solvent thereby exchanging the solvents and allowing the layer to be subsequently dried without restraint. Not all the non-volatile solvent, however, need be removed from the layer during the solvent exchange. Small amounts of non-volatile solvents may remain and act as a plasticizer to the polymer.

In some embodiments of the first method, the formed, phase separated article after the solvent removal, has a porosity of at least 5 (in some embodiments, at least 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90; in some embodiments, in a range from 25 to 90) percent. This porosity is caused by the phase separation of the polymer from the solvent, which initially leaves no unfilled voids as the pores in the polymer matrix composite are filled with solvent. After the solvent is completely or partly removed, void spaces in the polymer matrix composite are exposed. The particle-to-particle interactions can minimize the collapse or deformation of the porous polymer matrix composite from capillary-induced negative pressures from the solvent drying process.

In some embodiments of the first method, no solvent is removed from the formed article (even after inducing phase separation of the thermoplastic polymer from the solvent). This can be accomplished, for example, by using a non-volatile solvent (e.g., mineral oil or wax) and not completing the extraction/evaporation step.

Second Method

A second method of making polymer matrix composites described herein comprises:

combining (e.g., mixing or blending) a thermoplastic polymer, a solvent the thermoplastic polymer, and a plurality of dielectric particles to form a miscible thermoplastic polymer-solvent solution;

inducing phase separation of the thermoplastic polymer from the solvent; and

removing at least a portion of the solvent to provide the polymer matrix composite.

In some embodiments, the second method further comprises adding the dielectric particles to the miscible polymer-solvent solution, prior to phase separation. The polymeric network structure may be formed during the phase separation of the process. In some embodiments, the polymeric network structure is provided via an induced phase separation of a miscible thermoplastic polymer-solvent solution. In some embodiments, the phase separation is induced thermally (e.g., via thermally induced phase separation (TIPS) by quenching to lower temperature), chemically (e.g., via solvent induced phase separation (SIPS) by substituting a poor solvent for a good solvent), or change in the solvent ratio (e.g., by evaporation of one of the solvents). Other phase separation or pore formation techniques known in the art, such as discontinuous polymer blends (also sometimes referred to as polymer assisted phase inversion (PAPI)), moisture induced phase separation, or vapor induced phase separation, can also be used. The polymeric network structure may be inherently porous (i.e., have pores). The pore structure may be open, enabling fluid communication from an interior region of the polymeric network structure to an exterior surface of the polymeric network structure and/or between a first surface of the polymeric network structure and an opposing second surface of the polymeric network structure.

In some embodiments of the second method, the polymer in the miscible thermoplastic polymer-solvent solution has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted at at least one temperature above the melting point of the miscible thermoplastic polymer-solvent solution, and below the boiling point of the solvent.

In some embodiments of the second method, the polymer in the miscible thermoplastic polymer-solvent solution has a melting point, and wherein inducing phase separation is conducted at at least one temperature less than the melting point of the polymer in the miscible thermoplastic polymer-solvent solution. The thermoplastic polymer-solvent mixture may be heated to facilitate the dissolution of the thermoplastic polymer in the solvent. After the thermoplastic polymer has been phase separated from the solvent, at least a portion of the solvent may be removed from the polymer matrix composite using techniques known in the art, including evaporation of the solvent or extraction of the solvent by a higher vapor pressure, second solvent, followed by evaporation of the second solvent. In some embodiments, in a range from 10 to 100 (in some embodiments, in a range from 20 to 100, 30 to 100, 40 to 100, 50 to 100, 60 to 100, 70 to 100, 80 to 100, 90 to 100, 95 to 100, or even 98 to 100) percent by weight of the solvent, and second solvent, if used, may be removed from the polymer matrix composite.

The solvent is typically selected such that it is capable of dissolving the polymer and forming a miscible polymer-solvent solution. Heating the solution to an elevated temperature may facilitate the dissolution of the polymer. In some embodiments, combining the polymer and solvent is conducted at at least one temperature in a range from 20° C. to 350° C. The dielectric particles may be added at any or all of the combining, before the polymer is dissolved, after the polymer is dissolved, or at any time there between.

In some embodiments, the solvent is a blend of at least two individual solvents. In some embodiments, when the polymer is a polyolefin (e.g., at least one of polyethylene or polypropylene), the solvent may be at least one of mineral oil, paraffin oil/wax, camphene, orange oil, vegetable oil, castor oil, or palm kernel oil. In some embodiments, when the polymer is polyvinylidene fluoride, the solvent is at least one of ethylene carbonate, propylene carbonate, or 1,2,3 triacetoxypropane.

In some embodiments, the solvent may be removed, for example, by evaporation, high vapor pressure solvents being particularly suited to this method of removal. If the first solvent, however, has a low vapor pressure, a second solvent, of higher vapor pressure, may be used to extract the first solvent, followed by evaporation of the second solvent. For example, in some embodiments, when mineral oil is used as a first solvent, isopropanol at elevated temperature (e.g., about 60° C.) or a blend of methyl nonafluorobutyl ether (C₄F₉OCH₃), ethylnonafluorobutyl ether (C₄F₉OC₂H₅), and trans-1,2-dichloroethylene (available under the trade designation “NOVEC 72DE” from 3M Company, St. Paul, Minn.) may be used as a second solvent to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, when at least one of vegetable oil or palm kernel oil is used as the first solvent, isopropanol at elevated temperature (e.g. about 60° C.) may be used as the second solvent. In some embodiments, when ethylene carbonate is used as the first solvent, water may be used as the second solvent.

Typically, in the phase separation process, the blended mixture is formed in to a layer prior to solidification of the polymer. The polymer is dissolved in solvent (that allows formation of miscible thermoplastic-solvent solution), and the dielectric particles dispersed to form a blended mixture, that is formed into an article (e.g., a layer), followed by phase separation (e.g., temperature reduction for TIPS, solvent evaporation or solvent exchange with nonsolvent for SIPS). The layer-forming may be conducted using techniques known in the art, including, knife coating, roll coating (e.g., roll coating through a defined nip), and extrusion (e.g., extrusion through a die (e.g., extrusion through a die having the appropriate layer dimensions (i.e., width and thickness of the die gap))). In one exemplary embodiment, the mixture has a paste-like consistency and is formed in to a layer by extrusion (e.g., extrusion through a die having the appropriate layer dimensions (i.e., width and thickness of the die gap)).

After forming the slurry in to a layer, where the thermoplastic polymer is miscible in its solvent, the polymer is then induced to phase separate. Several techniques may be used to induce phase separation, including at least one of thermally induced phase separation or solvent induced phase separation. Thermally induced phase separation may occur when the temperature at which induced phase separation is conducted is lower than the combining temperature of the polymer, solvent, and dielectric particles. This may be achieved by cooling the miscible polymer-solvent solution, if combining is conducted near room temperature, or by first heating the miscible polymer-solvent solution to an elevated temperature (either during combining or after combining), followed by decreasing the temperature of the miscible polymer-solvent solution, thereby inducing phase separation of the thermoplastic polymer. In both, cases the cooling may cause phase separation of the polymer from the solvent. Solvent induced phase separation can be conducted by adding a second solvent, a poor solvent for the polymer, to the miscible polymer-solvent solution or may be achieved by removing at least a portion of the solvent of the miscible polymer-solvent solution (e.g., evaporating at least a portion of the solvent of the miscible polymer-solvent solution), thereby inducing phase separation of the polymer. Combination of phase separation techniques (e.g., thermally induced phase separation, and solvent induced phase separation), may be employed. Thermally induced phase separation, may be advantageous, as it also facilitates the dissolution of the polymer when combining is conducted at an elevated temperature. In some embodiments, thermally inducing phase separation is conducted at at least one temperature in a range from 5 to 300 (in some embodiments, in a range from 5 to 250, 5 to 200, 5 to 150, 15 to 300, 15 to 250, 15 to 200, 15 to 130, or even 25 to 110) ° C. below the combining temperature.

After inducing phase separation, at least a portion of the solvent may be removed, thereby forming a porous polymer matrix composite layer having a polymeric network structure and a dielectric material distributed within the thermoplastic polymer network structure.

The solvent may be removed by evaporation, high vapor pressure solvents being particularly suited to this method of removal. If the first solvent, however, has a low vapor pressure, a second solvent, of higher vapor pressure, may be used to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, in a range from 10 to 100 (in some embodiments, in a range from 20 to 100, 30 to 100, 40 to 100, 50 to 100, 60 to 100, 70 to 100, 80 to 100, 90 to 100, 95 to 100, or even 98 to 100) percent by weight of the solvent, and second solvent, if used, may be removed from the polymer matrix composite.

In some embodiments, the first and second methods further comprises compressing the polymer matrix composite. That is, after inducing phase separation, the formed polymeric network structure may be compressed, for example, to tune the air flow resistance of the polymer matrix composite. Compression of the polymer matrix composite may be achieved, for example, by conventional calendaring processes known in the art.

In some embodiments, where the network structure is plastically deformed by at least a compressive force, vibratory energy may be imparted during the application of the compressive force. In some of these embodiments, the polymer composite is in the form of a strip of indefinite length, and the applying of a compressive force step is performed as the strip passes through a nip. A tensile loading may be applied during passage through such a nip. For example, the nip may be formed between two rollers, at least one of which applies the vibratory energy; between a roller and a bar, at least one of which applies the vibratory energy; or between two bars, at least one of which applies the vibratory energy. The applying of the compressive force and the vibratory energy may be accomplished in a continuous roll-to-roll fashion, or in a step-and-repeat fashion. In other embodiments, the applying a compressive force step is performed on a discrete layer between, for example, a plate and a platen, at least one of which applies the vibratory energy. In some embodiments, the vibratory energy is in the ultrasonic range (e.g., 20 kHz), but other ranges are considered to be suitable. For further details regarding plastically deforming the network structure, see co-pending application having U.S. Ser. No. 62/578,732, filed Oct. 30, 2017, the disclosure of which is incorporated by reference.

In some embodiments, the density of the compressed polymer matrix composite is at least 1 (in some embodiments, at least 2, 3, 4, 5, 6, 7, 8, 9, or even at least 10; in some embodiments, in the range from 1 to 10, 1 to 9, 3 to 8, or even 4 to 7) g/cm³ after compression.

In some embodiments, polymer matrix composite described herein can be wrapped around a 0.5 mm (in some embodiments, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 1 cm, 5 cm, 10 cm, 25 cm, 50 cm, or even 1 meter) rod without breaking.

Polymer matrix composites comprising dielectric particles are useful, for example, as an electric field insulator, for example, in electronic articles (e.g., displays, electrical power grid components (e.g., transformer), and electric motors (e.g., for electric vehicles)). In some embodiments, an electronic article comprises a substrate, a conductive element adjacent to the substrate, a polymer matrix composite comprising dielectric particles described herein, wherein the polymer matrix composite has first and second, opposed major surfaces, wherein the first major surface adjacent to at least a portion of the conductive element and wherein an electrically-active layer is adjacent to at least portion of the second major surface of the polymer matrix composite.

Polymer matric composites comprising dielectric particles described herein can be used for, for example, high dielectric constant cable accessories to control electric filed stresses built up at locations of splices and termination. Further details on high dielectric constant cable accessories in general can be found, for example, in U.S. Pat. No. 8,974,706 (Somasiri, et al.).

Polymer matrix composites comprising dielectric particles can be used, for example, for microwave lenses and antennas that require microwave transmissive high dielectric constant materials that contain high dielectric constant particles having low density and low microwave loss. Details on microwave lenses and antennas in general can be found, for example, in U.S. Pat. No. 6,562,448 (Chamberlain et al.) and “Dielectric materials for wireless communication,” Mailadil T. Sebastian, Elsevier, 2008.

Polymer matrix composites containing dielectric particles can also be used, for example, for electromagnetic radiation absorbers (e.g., for radar absorbing and electronic device shielding). Further details on radar absorbing and electronic device shielding in general can be found, for example, in U.S. Pat. No. 5,389,434 (Chamberlain et al.).

EXEMPLARY EMBODIMENTS

1A. A polymer matrix composite comprising:

a porous polymeric network structure; and

a plurality of dielectric particles distributed within the polymeric network structure, wherein the dielectric particles are present in a range from 5 to 98, 10 to 98, 20 to 98, 25 to 98, 50 to 98, 75 to 98, 80 to 98, 90 to 98, or even 95 to 98) weight percent, based on the total weight of the dielectric particles and the polymer (excluding any solvent); and wherein the polymer matrix composite has a dielectric constant in a range from 1.05 to 80 (in some embodiments, in a range from 1.05 to 80 (in some embodiments, in a range from 1.1 to 80, 1.15 to 80, 1.2 to 80, 1.1 to 75, 1.15 to 75, 1.2 to 75, 1.2 to 70, 1.1 to 70, 1.15 to 70, 1.2 to 65, 1.1 to 65, 1.15 to 65, 1.2 to 60, 1.1 to 60, 1.15 to 60, 1.2 to 55, 1.1 to 55, 1.15 to 55, 1.2 to 50, 1.1 to 50, 1.15 to 50, 1.2 to 45, 1.1 to 45, 1.15 to 45, 1.2 to 40, 1.1 to 40, 1.15 to 40, 1.2 to 35, 1.1 to 35, 1.15 to 35, 1.2 to 30, 1.1 to 30, 1.15 to 30, 1.2 to 25, 1.1 to 25, 1.15 to 25, 1.2 to 20, or even 1.1 to 20, 1.15 to 20, 1.2 to 20).

2A. The polymer matrix composite of Exemplary Embodiment 1A having a density in a range from 0.05 to 6 (in some embodiments, in a range from 0.05 to 5, 0.05 to 3, 0.05 to 2.5, 0.05 to 2, 0.05 to 1, or even 0.05 to 0.2) gicm³. 3A. The polymer matrix composite of any preceding A Exemplary Embodiment having a density of at least 1 (in some embodiments, at least 4, or even at least 6; in some embodiments, in a range from 1 to 6, or even 4 to 6) g/cm³. 4A. The polymer matrix composite of any preceding A Exemplary Embodiment having a porosity of at least 5 (in some embodiments, at least 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90; in some embodiments, in a range from 25 to 90) percent. 5A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the dielectric particles comprise at least one of barium titanate, alumina, titania, or CaCu₃Ti₄O₁₂. 6A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the dielectric particles comprise glass bubbles each having a first major surface coated with a layer comprising at least one metal (e.g., aluminum), and a layer comprising at least one metal oxide (e.g., aluminum oxide) coated on to the layer comprising at least one metal. 7A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the dielectric particles comprise glass beads each having a first major surface coated with a layer comprising at least one metal (e.g., aluminum), and a layer comprising at least one metal oxide (e.g., aluminum oxide) coated on to the layer comprising at least one metal. 8A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the dielectric particles have an average particle size (average length of longest dimension) in a range from 10 nm to 120 micrometers (in some embodiments, in a range from 50 nm to 100 nm, 15 micrometers to 125 micrometers, or even 30 micrometers to 60 micrometers). 9A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the porous polymeric network structure comprises at least one of polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, polymethacrylate, polyacrylonitrile, polyolefin, styrene or styrene-based random and block copolymer, chlorinated polymer, fluorinated polymer, or copolymers of ethylene and chlorotrifluoroethylene. 10A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the porous polymeric network structure comprises a phase-separated plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs). 11A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the porous polymeric network structure comprises a polymer having a number average molecular weight in a range from of 5×10⁴ to 1×10⁷ (in some embodiments, in a range from 1×10⁶ to 8×10⁶, 2×10⁶ to 6×10⁶, or even 3×10⁶ to 5×10⁶) g/mol. 12A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the polymer matrix composite is in the form of a layer having a thickness in a range from 50 to 7000 micrometers. 13A. The polymer matrix composite of any preceding A Exemplary Embodiment, wherein the porous polymeric network structure is produced by an induced phase separation of a miscible thermoplastic polymer-solvent solution. 14A. The polymer matrix composite of Exemplary Embodiment 13A, wherein induced phase separation is at least one of thermally induced phase separation and solvent induced phase separation. 15A. The polymer matrix composite of any preceding A Exemplary Embodiment having first and second planar, opposed major surfaces. 16A. The polymer matrix composite of any preceding A Exemplary Embodiment, further comprising a reinforcement (e.g., attached to the polymer matrix composite, partial therein, and/or therein). 17A. The polymer matrix composite of any preceding A Exemplary Embodiment that can be wrapped around a 0.5 mm (in some embodiments, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 1 cm, 5 cm, 10 cm, 25 cm, 50 cm, or even 1 meter) rod without breaking. 18A. The polymer matrix composite of any preceding A Exemplary Embodiment comprising at least one of a viscosity modifier (e.g., fumed silica, block copolymers, and wax), a plasticizer, a thermal stabilizer (e.g., such as available, for example, under the trade designation “IRGANOX 1010” from BASF, Ludwigshafen, Germany), an antimicrobial (e.g., silver and quaternary ammonium), a flame retardant, an antioxidant, a dye, a pigment, or an ultraviolet (UV) stabilizer. 1B. A method of making the polymer matrix composite of any preceding A Exemplary Embodiment, the method comprising:

combining (e.g., mixing or blending) a thermoplastic polymer, a solvent, and a plurality of dielectric particles to provide a slurry;

forming the slurry in to an article (e.g., a layer);

heating the article in an environment to retain at least 90 (in some embodiments, at least 91, 92, 93, 94, 95, 96, 97, 98, 99, or even at least 99.5) percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) percent of the thermoplastic polymer, based on the total weight of the thermoplastic polymer; and

inducing phase separation of the thermoplastic polymer from the solvent to provide the polymer matrix composite.

2B. The method of Exemplary Embodiment 1B, further comprising removing at least a portion (in some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100 percent by weight of the solvent, based on the weight of the solvent in the formed article) of the solvent from the formed article, after inducing phase separation of the thermoplastic polymer from the solvent. 3B. The method of Exemplary Embodiment 2B, wherein at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, is removed, wherein the formed article, before removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, of the solvent has a first volume, wherein the formed article, after removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, has a second volume, and wherein the difference between the first and second volume (i.e., (the first volume minus the second volume) divided by the first volume times 100) is less than 10 (in some embodiments, less than 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.75, 0.5, or even less than 0.3) percent. 4B. The method of Exemplary Embodiment 3B, wherein the article has first and second major surfaces with ends perpendicular to the first and second major surfaces, and where the ends are unrestrained during the solvent removal. 5B. The method of either Exemplary Embodiment 3B or 4B, wherein the formed article, after the solvent removal, has a porosity of at least 5 (in some embodiments, at least 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90; in some embodiments, in a range from 25 to 90) percent. 6B. The method of Exemplary Embodiment 1B, wherein no solvent is removed from the formed article (even after inducing phase separation of the thermoplastic polymer from the solvent). 7B. The method of any preceding B Exemplary Embodiment, wherein inducing phase separation includes thermally induced phase separation. 8B. The method of any preceding B Exemplary Embodiment, wherein the polymer in the slurry has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted below the melting point of the polymer in the slurry, and below the boiling point of the solvent. 9B. The method of any preceding B Exemplary Embodiment, wherein the polymer in the slurry has a melting point, and wherein inducing phase separation is conducted at less than the melting point of the polymer in the slurry. 10B. The method of any preceding B Exemplary Embodiment, further comprising compressing the polymer matrix composite. 11B. The method of any of Exemplary Embodiments 1B to 9B, further comprising applying vibratory energy to the polymer matrix composite simultaneously with the applying a compressive force. 12B. The method of any preceding B Exemplary Embodiment, wherein the porous polymeric network structure comprises at least one of polyacrylonitrile, polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, polymethacrylate, polyolefin, styrene or styrene-based random and block copolymer, chlorinated polymer, fluorinated polymer, or copolymers of ethylene and chlorotrifluoroethylene. 13B. The method of any preceding B Exemplary Embodiment, wherein the porous polymeric network structure comprises a plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs). 14B. The method of any preceding B Exemplary Embodiment, wherein the porous polymeric network structure is produced by an induced phase separation of a miscible thermoplastic polymer-solvent solution. 15B. The method of Exemplary Embodiment 14B, wherein inducing phase separation includes thermally induced phase separation. 1C. A method of making the polymer matrix composite of any preceding A Exemplary Embodiment, the method comprising:

combining (e.g., mixing or blending) a thermoplastic polymer, a solvent the thermoplastic polymer, and a plurality of dielectric particles to form a miscible thermoplastic polymer-solvent solution;

inducing phase separation of the thermoplastic polymer from the solvent; and

removing at least a portion of the solvent to provide the polymer matrix composite.

2C. The method of Exemplary Embodiment 1C, wherein inducing phase separation includes at least one of thermally induced phase separation or solvent induced phase separation. 3C. The method of Exemplary Embodiment 1C, wherein the polymer in the miscible thermoplastic polymer-solvent solution has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted above the melting point of the miscible thermoplastic polymer-solvent solution and below the boiling point of the solvent. 4C. The method of any preceding C Exemplary Embodiment, wherein the polymer in the miscible thermoplastic polymer-solvent solution has a melting point, and wherein inducing phase separation is conducted at less than the melting point of the polymer in the miscible thermoplastic polymer-solvent solution. 5C. The method of any preceding C Exemplary Embodiment, further comprising compressing the polymer matrix composite. 6C. The method of any of Exemplary Embodiments 1C to 4C, further comprising applying vibratory energy to the polymer matrix composite simultaneously with the applying a compressive force. 7C. The method of any preceding C Exemplary Embodiment, wherein the porous polymeric network structure comprises at least one of polyacrylonitrile, polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, polymethacrylate, polyolefin, styrene or styrene-based random and block copolymer, chlorinated polymer, fluorinated polymer, or copolymers of ethylene and chlorotrifluoroethylene. 8C. The method of any preceding C Exemplary Embodiment, wherein the porous polymeric network structure comprises a plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs). 1D. An electric field insulator comprising the polymer matrix composite of any preceding A Exemplary Embodiment.

Advantages and embodiments of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated.

EXAMPLES Air Flow Resistance Test

Air flow resistance was measured using a densitometer (obtained as Model 4110 from Gurley Precision Instruments, Troy, N.Y.) with a timer (obtained as Model 4320 from Gurley Precision Instruments). A sample was clamped in the tester. The timer and photo eye were reset and the cylinder was released, allowing air to pass through a 1 square inch (6.5 cm²) circle with a constant force of 4.88 inches (12.4 cm) of water (1215 N/m²). The time to pass 50 cm³ of air was recorded.

Bubble Point Pressure Test

Bubble point pressure is a commonly used technique to characterize the largest pore in a porous membrane. Discs 47 mm in diameter were cut and samples soaked in mineral oil to fully fill and wet out the pores within the sample. The wet samples were then placed in a holder (47 mm; Stainless Holder Part #2220 from Pall Corporation, Port Washington, N.Y.). Pressure was slowly increased on the top of the sample using a pressure controller and gas flow was measured on the bottom with a gas flow meter. The pressure was recoded when there was a significant increase in flow from the baseline flow rate. This was reported as the bubble point pressure pounds per square inch (psi) (centimeters of mercury, cm Hg or Pascals, Pa.). This technique was a modification to ASTM F316-03 (2006), “Standard Test Methods for Pore Size Characteristics of Membrane Filters by Bubble Point and Mean Flow Pore Test,” the disclosure of which is incorporated herein by reference, and included an automated pressure controller and flow meter to quantify when the bubble point pressure had been reached. The pore size was calculated per the ASTM using the following equation:

Limiting Pore Diameter (μm)=(Surface Tension in dynes/cm*0.415)/(Pressure in psi).

The factor of 0.415 was included since the pressure was in units of psi. A surface tension of 34.7 dynes/cm was used for the mineral oil.

Density and Porosity Test

The density of a sample was calculated using a method similar to ASTM F-1315-17 (2017), “Standard Test Method for Density of a Sheet Gasket Material,” the disclosure of which is incorporated herein by reference, by cutting a 47 mm diameter disc, weighing the disc on an analytical balance of suitable resolution (typically 0.0001 gram), and measuring the thickness of the disc on a thickness gauge (obtained as Model 49-70 from Testing Machines, Inc., New Castle, Del.) with a dead weight of 7.3 psi (50.3 KPa) and a flat anvil of 0.63 inch (1.6 cm) diameter, with a dwell time of about 3 seconds and a resolution of +/−0.0001 inch. The density was then calculated by dividing the mass by the volume, which was calculated from the thickness and diameter of the sample. With the known densities and weight fractions of the components of the polymer matrix composite, the theoretical density of the polymer matrix composite was calculated by the rule of mixtures. Using the theoretical density and the measured density, the porosity was calculated as:

Porosity=[1−(measured density/theoretical density)]×100.

Dielectric Test

Sample was placed between two gold plated electrodes. The positive electrode was 2.54 cm (1 inch) diameter and the ground electrode was 5.1 cm (2 inch) diameter. A 1400-gram weight is placed on the electrode for good contact. The positive electrode was connected to the positive terminal and the ground electrode was connected to the negative terminal of an inductance-capacitance-resistance (LCR) meter (obtained as Model 72-960 from Tenma, Tokyo, Japan). Frequency was selected at 1 kHz, and the capacitance in pF (picofarad) was recorded directly from the display.

The dielectric constant (K) was calculated from the measured capacitance (C) using the following equation.

K=C*d/e ₀ *A

where d was thickness of the sample in meters, A was area of cross section in square meters and e₀=8.85 pF/m, permittivity of free space.

Complex Permittivity Test

The complex electric permittivity (dielectric constant and dielectric loss tangent) were measured, at a frequency of 9.5 GHz, using the split post dielectric resonator method similar to that found in ASTM D2520-13 Method B (2018), “Standard Test Methods for Complex Permittivity (Dielectric Constant) of Solid Electrical Insulating Materials at Microwave Frequencies and Temperatures to 1650° C.” and United States Department of Commerce National Institute of Standards and Technology, “NIST Technical Note 1512, Dielectric and Magnetic Properties of Printed Wiring Boards and Other Substrate Materials, Section 3.2.3,” James Baker-Jarvis, et al., March 1999, the disclosures of which is incorporated here by reference.

Specifically, five 40 mm diameter discs were punched from the sample sheet. The thickness of the discs was measured with a hand-held thickness gauge (obtained as Model No. 293-832 from Mitutoyo America Corporation, Aurora, Ill.). The average thickness was reported. The split post dielectric resonator of the desired frequency (obtained from QWED Company, Warsaw, Poland) was connected to the vector network analyzer (obtained as Model E8364C 10 MHz-50 GHz PNA Network Analyzer, from Keysight/Agilent Technologies, Santa Rosa, Calif.). The resonance band width and resonance frequency of the cavity was accurately measured with the magnitude of the Transmission S-Parameter defined as S21, empty and with samples inserted one at a time. Using the four electronics measurements described in the references above, the complex permittivity was calculated with the QWED software at each frequency for each cavity. Measurements near 10 GHz are accomplished with a split post dielectric resonator design of the following air gap hg=1 mm; active area dimension L_(l)=25 mm, and dimension L_(f)<150 mm, parameters. These parameters and the measurement technique have been described in the Keysight Application instructions titled “Split Post Dielectric Resonators for Dielectric Measurements of Substrates,” published Dec. 2, 2017, the disclosure of which is incorporated herein by reference. The complex electric permittivity was calculated with the Keysight-Agilent Software 85071E that accompanied the resonance frequency of the cavity.

Example 1

A 120-milliliter (4-ounce) glass jar was charged with 1.5 gram of an ultra-high molecular weight polyethylene (UHMWPE) (obtained under the trade designation “GUR-2126” from Celanese Corporation, Irving, Tex.), and 15 grams of aluminum and aluminum oxide coated glass bubbles (the glass bubbles were obtained under the trade designation “3M SCOTCHLITE S60 GLASS BUBBLES” from 3M Company, St. Paul, Minn.), and coated as described for the Examples of U.S. Pat. No. 8,698,394 (McCutcheon et al.), the disclosure of which is incorporated herein by reference) and shook with an acoustic mixer (obtained under the trade designation “LABRAM RESONATACOUSTIC MIXER” from Resodyn Inc., Butte, Mont.) at 70% intensity for 1 minute. 17.5 grams of a low odor kerosene (obtained from Alfa Aesar, Ward Hill, Mass.) was added to this mixture and stirred by hand with a spatula until a uniform slurry was obtained. The slurry was applied with a scoop at room temperature (about 25° C.) to a 3-mil (75-micrometer) heat stabilized polyethylene terephthalate (PET) liner (obtained under the trade designation “COATED PET ROLL #33716020500” from 3M Company) then a 3-mil (75-micrometer) heat stabilized PET liner was applied on the top to sandwich the slurry. The slurry was then spread between the PET liners by using a notch bar set to a gap of 36 mils (914.4 micrometers). The notch bar rails were wider than the PET liner to obtain an effective wet film thickness of 30 mils (762 micrometers). Progressive multiple passes with increasing downward pressure of the notch bar were used to flatten the slurry. The sandwiched, formed slurry was placed on an aluminum tray and placed in a lab oven (obtained under the trade designation “DESPATCH RFD1-42-2E” from Despatch, Minneapolis, Minn.), at 135° C. (275° F.) for 5 minutes to activate (i.e., to allow the UHMWPE to dissolve into the solvent forming a single phase). The tray with the activated sandwiched, formed slurry was removed from the oven and allowed to air cool to ambient temperature (about 25° C.), forming a solvent filled polymer matrix composite. Both the top and bottom liners were removed exposing the polymer matrix composite to air. The polymer matrix composite was then placed back on a PET liner (“COATED PET ROLL #33716020500”) on the tray and the tray was inserted into the lab oven (“DESPATCH RFD1-42-2E”) at 100° C. (215° F.) for an hour. After evaporation, the polymer matrix composite was removed from the oven, allowed to cool to ambient temperature, and characterized.

Referring to FIG. 1, a scanning electron microscope (SEM) digital image of a cross-section of the polymer matrix composite taken with a SEM (obtained under the trade designation “PHENOM” from FEI Company, Hillsboro, Oreg.) is shown. The cross-sectional sample was prepared by liquid nitrogen freeze fracturing followed by gold sputter coating with a sputter coater (obtained under the trade designation “EMITECH K550X” from Quorum Technologies, Laughton East Sussex, England).

The resulting polymer matrix composite was 32.5 mils (826 micrometers) thick, had a measured density of 0.36 g/cm³, (as determined by the “Density and Porosity Test”), a porosity of 42.9% (as determined by the “Density and Porosity Test”), a pore size of 28.8 micrometers (as determined by the “Bubble Point Pressure Test”), a Gurley air flow of 21.1 sec/50 cm³ (as determined by the “Air Flow Resistance Test”), a capacitance of 92 picofarad (as determined by the “Dielectric Test”), and a dielectric constant of 17.0 (as determined by the “Dielectric Test”). The dielectric characterization data for the first five examples were reported in Table 1, below.

TABLE 1 Neat Coated “S60 Exam- Glass Glass Thickness, ple UHMWPE, Bubbles, Bubbles,” Kerosene, micrometers Capacitance, Dielectric No. g g g g (mils) pf Constant 1 1.5 15  0 17.5 826 (32.5) 92 17 2 1.5 11.25  3.75 17.5 813 (32) 75 13.6 3 1.5  7.5  7.5 17.5 785 (30.9) 50  8.8 4 1.5  3.75 11.25 17.5 742 (29.2) 42  7 5 1.5  0 15 17.5 803 (31.6) 41  7.3

Example 2

Example 2 was prepared and tested as described for Example 1, except 25% weight of the coated glass bubbles were replaced with uncoated glass bubbles (“3M SCOTCHLITE S60 GLASS BUBBLES”).

The resulting polymer matrix composite was 32.0 mils (813 micrometers) thick, had a measured density of 0.36 g/cm³, a porosity of 42.9%, a pore size of 36 micrometers, a Gurley air flow of 52.1 sec/50 cm³, and a dielectric constant of 13.6. The dielectric characterization data for Example 2 is reported in Table 1, above.

Example 3

Example 3 was prepared and tested as described for Example 1, except 50% weight of the coated glass bubbles were replaced with uncoated glass bubbles (“3M SCOTCHLITE S60 GLASS BUBBLES”).

The resulting polymer matrix composite was 30.9 mils (785 micrometers) thick, had a measured density of 0.36 g/cm³, a porosity of 42.9%, a pore size of 12 micrometers, a Gurley air flow of 56.8 sec/50 cm³, and a dielectric constant of 8.8. The dielectric characterization data for Example 3 is reported in Table 1, above.

Example 4

Example 4 was prepared and tested as described for Example 1, except 75% weight of the coated glass bubbles were replaced with uncoated glass bubbles (“3M SCOTCHLITE S60 GLASS BUBBLES”).

The resulting polymer matrix composite was 28.7 mils (729 micrometers) thick, had a measured density of 0.35 g/cm³, a porosity of 44.4%, a pore size of 48 micrometer, a Gurley air flow of 26.4 sec/50 cm³, and a dielectric constant of 6.75. The dielectric characterization data for Example 4 is reported in Table 1, above.

Example 5

Example 5 was prepared and tested as described for Example 1, except all of the dielectric particles were uncoated glass bubbles (“3M SCOTCHLITE S60 GLASS BUBBLES”).

The resulting polymer matrix composite was 30.4 mils (772 micrometers) thick, had a measured density of 0.33 g/cm³, a porosity of 47.9%, a pore size of 6.9 micrometers, a Gurley air flow of 20.2 sec/50 cm³, and a dielectric constant of 7.3. The dielectric characterization data for Example 5 is reported in Table 1, above.

Examples 6-10

Examples 6-10 were prepared as described for Examples 1-5, respectively, except the coated glass bubbles were replaced with barium titanate (obtained under the trade designation “99% BaTiO₃ A0882” from GFS Chemicals, Columbus, Ohio) and the uncoated glass bubbles were replaced with 60-micrometer polyamide particles (obtained under the trade designation “ORGASOL 2002 ES 6 NAT 3” from Arkema, King of Prussia, Pa.). The total weight of the binder, particles and diluent (slurry) in the jar was also adjusted taking account for the particle's change in volume and wetting characteristics. The weights of the polymer binder, particles and diluent are given in Table 2, below.

TABLE 2 Exam- Polyamide Thickness, ple UHMWPE, BaTiO₃, Particle, Kerosene, micrometers Capacitance Dielectric No. g g g g (mils) pf Constant  6 1.5 25  0 17.0  655 (25.8)  42.7 6.2  7 1.5 18.75  6.25 17.0  820 (32.3)  32.7 6.0  8 1.5 12.5 12.5 17.0  942 (37.1)  20.0 4.2  9 1.5  6.25 18.75 21.0 1029 (40.5)  20.6 4.7 10 1.5  0 25 24.0 1118 (44.0) 197 4.9

The dielectric measurements and results from the polymer matrix composites were recorded in Table 2 (above) from 47 mm disks that were punched out.

The samples that were made and tested in Table 2 (above) were then compressed in a hydraulic press (obtained under the trade designation “WABASH-GENESIS MODEL G30H-15-LP” from Wabash MPI, Wabash, Ind.) with 27,215 kilograms (30 tons) pressure between steel plates for 30 seconds at ambient temperature (about 25° C.). The thickness and dielectric constants were measured again and recorded in Table 3, below.

TABLE 3 Exam- Polyamide Thickness, ple UHMWPE, BaTiO₃, Particle, Kerosene, micrometers Capacitance Dielectric No. g g g g (mils) pf constant  6 1.5 25  0 17.0 401 (15.8) 122.2 10.9  7 1.5 18.75  6.25 17.0 503 (19.8)  31.3  3.5  8 1.5 12.5 12.5 17.0 538 (21.2)  31.1  3.7  9 1.5  6.25 18.75 21.0 569 (22.4)  34.5  4.4 10 1.5  0 25 24.0 625 (24.6)  30.5  4.0

Examples 11 and 12

Examples 11 and 12 were prepared and tested as described for Example 6, except the barium titanate concentration was increased as shown in Table 4, below.

TABLE 4 Exam- Polyamide Thickness, ple UHMWPE, BaTiO₃, Particle, Kerosene, micrometers Capacitance, Dielectric No. g g g g (mils) f Constant 11 1.5 50 0 32.0 597 (23.5) 64.2  8.6 12 1.5 75 0 50.0 620 (24.4) 83.2 11.5

Example 13

Example 13 was prepared as described for Example 1, except the weight of the low odor kerosene was replaced with mineral oil (obtained under the trade designation “KAYDOL” (Product Number 637760) from Brenntag Great Lakes Inc., Wauwatosa, Wis.). The mineral oil was exchanged using isopropyl alcohol before the evaporation step.

Referring to FIG. 2, a SEM digital image of a cross-section of the polymer matrix composite is shown.

The resulting polymer matrix composite was 33.1.0 mils (841 micrometers) thick and a Gurley air flow of 50.5 sec/50 cm³.

Example 14

Example 14 was prepared as described for Example 1, except the weight of the UHMWPE (“GUR-2126”) used was 21 grams and the low odor kerosene was 21 grams.

Referring to FIG. 3, a SEM digital image of a cross-section of the polymer matrix composite is shown.

The resulting polymer matrix composite was 33.0 mils (838 micrometers) thick.

Example 15

A 4 gallon (15.1 liter) double planetary mixer (obtained under the trade designation “DPM-4” from Charles Ross & Son Company, Hauppauge, N.Y.) was charged with 66 grams of UHMWPE (“GUR-2126”), and 176 grams of glass bubbles (obtained under the trade designation “3M GLASS BUBBLES K1” from 3M Company, St. Paul, Minn.), and 1080 grams of paraffin (obtained under the trade designation “ISOPAR G” from Brenntag Great Lakes, Inc., Wauwatosa, Wis.). The components were mixed for 5 minutes at 40 rpm with full vacuum to form a uniform slurry. The slurry was then discharged into a 1 gallon (3.8 liter) can. The can was mixed with an air mixer to disperse the slurry. A 500 ml plastic beaker was then used to remove some of the slurry from the can. The slurry was applied with a scoop at room temperature (about 25° C.) to a 3 mil (75 micrometer) thick, 12 inches (30.5 cm) wide, heat stabilized polyethylene terephthalate (PET) liner (“COATED PET ROLL #33716020500”) then a 3-mil (75-micrometer), 12 inches (30.5 cm) wide, heat stabilized PET liner (“COATED PET ROLL #33716020500”) was applied to sandwich the slurry. The slurry was then spread between moving PET liners by conveying through a notch bar set to a gap of 15 mils (381 micrometers). The PET liners were pulled with a tension of 2.3 kg (5 pounds) from a winding stand. The sandwiched, formed slurry was conveyed at a speed of 6 feet per minute (1.8 meter per minute) through a the first two zones of a three-zone, 18 feet (5.5 meters) long, steam-heated, convection oven (obtained from Infratrol Oven Corporation, South Beloit, Ill.) at 135° C. (275° F.) to activate (i.e., to allow the UHMWPE to dissolve into the solvent). The activated sandwiched formed slurry was conveyed from the first two zones of the oven through an air nozzle to cool the film and enable removal of the top liner. The activated formed slurry and bottom liner re-entered the third, 18 feet long, oven zone at 104° C. (220° F.) and allowed the paraffin to evaporate. The activated formed, solvent dried polymer matrix composite was conveyed out of the 3^(rd) oven zone and allowed to air cool wound onto a roll to ambient temperature (about 25° C.). The bottom liner was removed exposing the polymer matrix composite to air. A sample of the polymer matrix composite was then placed on a PET liner (“COATED PET ROLL #33716020500”) on a tray and the tray was inserted into the lab oven (“DESPATCH RFD1-42-2E”) at 100° C. (215° F.) for an hour. After evaporation, the polymer matrix composite was removed from the oven, allowed to cool to ambient temperature, and characterized.

The resulting polymer matrix composite was 17.7 mils (449.6 micrometers) thick and had a measured density of 0.093 g/cm³, as determined by the “Density and Porosity Test;” and had a dielectric constant, Tan Delta, and thickness at 9.5 GHz of 1.12, 0.0011, and 0.381 mm, respectively, as determined by the “Complex Permittivity Test.”

Example 16

Example 16 was prepared as described for Example 15, except 1280 grams of paraffin (“ISOPAR G”) was used.

The resulting polymer matrix composite was 12.3 mils (312.4 micrometers) thick and had a measured density of 0.081 g/cm³, as determined by the “Density and Porosity Test;” and had a dielectric constant, Tan Delta, and thickness at 9.5 GHz of 1.11, 0.0010, and 0.369 mm, respectively, as determined by the “Complex Permittivity Test.”

Foreseeable modifications and alterations of this disclosure will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. 

1. A polymer matrix composite comprising: a porous polymeric network structure; and a plurality of dielectric particles distributed within the polymeric network structure, wherein the dielectric particles are present in a range from 5 to 98 weight percent, based on the total weight of the dielectric particles and the polymeric network structure; and wherein the polymer matrix composite has a dielectric constant in a range from 1.05 to 80, optionally wherein the polymer matrix composite has a density in a range from 0.05 to 6 g/cm³. 2-4. (canceled)
 5. The polymer matrix composite of claim 1, wherein the dielectric particles comprise at least one of barium titanate, alumina, titania, CaCu₃Ti₄O₁₂, or glass bubbles each having a first major surface coated with a layer comprising at least one metal, and a layer comprising at least one metal oxide coated on to the layer comprising at least one metal. 6-8. (canceled)
 9. The polymer matrix composite of claim 1, wherein the porous polymeric network structure comprises at least one of polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, polymethacrylate, polyacrylonitrile, polyolefin, styrene or styrene-based random and block copolymer, chlorinated polymer, fluorinated polymer, or copolymers of ethylene and chlorotrifluoroethylene.
 10. The polymer matrix composite of claim 1, wherein the porous polymeric network structure comprises phase separated plurality of interconnected morphologies.
 11. The polymer matrix composite of claim 1, wherein the porous polymeric network structure comprises a polymer having a number average molecular weight in a range from of 5×10⁴ to 1×10⁷ g/mol, and wherein the polymer matrix composite is in the form of a layer having a thickness in a range from 50 to 7000 micrometers.
 12. A method of making the polymer matrix composite of claim 1, the method comprising: combining a thermoplastic polymer, a solvent, and a plurality of dielectric particles to provide a slurry; forming the slurry into an article; heating the article in an environment to retain at least 90 percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 by weight percent of the thermoplastic polymer, based on the total weight of the thermoplastic polymer; and inducing phase separation of the thermoplastic polymer from the solvent to provide the polymer matrix composite, optionally further comprising removing at least a portion of the solvent from the formed article after inducing phase separation of the thermoplastic polymer from the solvent.
 13. The method of claim 12, further comprising removing at least a portion of the solvent from the formed article after inducing phase separation of the thermoplastic polymer from the solvent.
 14. The method of claim 13, wherein no solvent is removed from the formed article.
 15. The method of claim 12, wherein inducing phase separation includes thermally induced phase separation.
 16. The method of claim 12, wherein the thermoplastic polymer in the slurry has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted below the melting point of the thermoplastic polymer in the slurry, and below the boiling point of the solvent.
 17. The method of claim 12, wherein the thermoplastic polymer in the slurry has a melting point, and wherein inducing phase separation is conducted at less than the melting point of the thermoplastic polymer in the slurry.
 18. The method of claim 12, further comprising compressing the polymer matrix composite.
 19. The method of claim 12, further comprising applying vibratory energy to the polymer matrix composite simultaneously with the applying a compressive force.
 20. A method of making the polymer matrix composite of claim 1, the method comprising: combining a thermoplastic polymer, a solvent the thermoplastic polymer is soluble, and a plurality of dielectric particles to form a miscible thermoplastic polymer-solvent solution; inducing phase separation of the thermoplastic polymer from the solvent; and removing at least a portion of the solvent to provide the polymer matrix composite.
 21. The method of claim 20, wherein inducing phase separation includes at least one of thermally induced phase separation or solvent induced phase separation.
 22. The method of claim 20, wherein the thermoplastic polymer in the miscible thermoplastic polymer-solvent solution has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted at temperature above the melting point of the miscible thermoplastic polymer-solvent solution, and below the boiling point of the solvent.
 23. The method of claim 20, wherein the thermoplastic polymer in the miscible thermoplastic polymer-solvent solution has a melting point, and wherein inducing phase separation is conducted at less than the melting point of the thermoplastic polymer in the miscible thermoplastic polymer-solvent solution.
 24. The method of claim 20, further comprising compressing the polymer matrix composite.
 25. The method of claim 20, further comprising applying vibratory energy to the polymer matrix composite simultaneously with the applying a compressive force.
 26. An electric field insulator comprising the polymer matrix composite of claim
 1. 